Electrical transmissions are often used in applications such as locomotives or other large self-propelled traction vehicles. An example is described in U.S. Pat. No. 4,616,166.
Such a vehicle, in practice, will sometimes be out of service for maintenance. During maintenance, it is often necessary to position the crankshaft of a prime mover, such as a diesel engine, at a specific position, e.g., such that a piston in a specified cylinder is at top or bottom dead center. Usually, this operation is performed by using a long metal bar as a lever to manually rotate a ring gear attached to the crankshaft, an operation known as “barring,” or by otherwise engaging a flywheel coupled to crankshaft 23 (FIG. 1) to move the crankshaft. For example, a barring rig consisting of a pinion gear and an air motor may be coupled to a ring gear of the engine, Then, measured amounts of air pressure are supplied to the rig to slowly rotate the engine until the crankshaft, in the operator's estimation, is at the desired position. Although it is known in the art to employ the electrical machine as a cranking motor to start the engine, such cranking operation cannot be performed with sufficient precision to replace a barring operation. It is therefore desirable to provide improved apparatus and methods for precisely positioning the crankshaft.
When the engine exhibits reduced performance, diagnostic procedures, such as cylinder compression measurements are performed. Such measurements also require extensive manual operations. Thus, it is also desirable to provide improved apparatus and methods for diagnosis and determination of causes of performance degradation in the engine.